Cluster primary ions

F. Kollmer, Cluster primary ion bombardment of organic materials, Applied Surface Science, 231 232, 153 158 (2004). 

Investigations of cluster formation serve to explain the evaporation and atomization of sample material and ion formation processes. A further aim of cluster research is to find out under what conditions cluster or polyatomic ion formation can be influenced in order to avoid disturbing interferences and decrease the detection limits of elements. On the other hand, polyatomic ions have also been used as analyte ions for analysis, e.g. the application of MCs+ and MCs2+ dimeric and trimeric ions as analyte11 or of cluster primary ion beams (e.g., of bismuth and gold primary clusters)15 16 by the bombardment and sputtering of a solid surface in SIMS.17-21 Especially in SIMS, a multitude of cluster ions with high ion formation rates are observed.18 22 23... 

Currently, cluster primary ions [6-12] such as AUx (the gold cluster ion), Bix (the bismuth cluster ion), and Ceo [1,13,14], which produce larger fragment ions from proteins, are employed in the analysis of biomaterials... 

Gillen, G, King, L., Freibanm, B., Larean, R., Bennett, X, Chmara, F. (2001) Negative cesinm spntter ion source for generating cluster primary ion beams for secondary ion mass spectrometry analysis. J. Vac. Sci. Technol. A, 19, 568-575. 

Seah MP (2007) Cluster ion sputtering molecular ion yield relationships for different cluster primary ions in static SIMS of organic materials. Surf Interface Anal 39 890-897. doi 10.1002/ sia.2609... 

An exception to the above rule (the access to molecular information in Dynamic SIMS) is noted when using large cluster primary ions (C, Ar , etc., where n can equal several thousands). This is realized because these ions introduce the possibility of molecular depth profiling and imaging. Cluster ion beams can also be used to examine surface distributions under Static-like conditions. As a result, the use of cluster ion beams in SIMS opens many new fields of application (Mahoney 2013). 

Traditionally, SIMS has been subdivided into the areas otherwise referred to as Static SIMS and Dynamic SIMS. Static SIMS analyzes the undisturbed population of elements and molecules that are present at the outermost surface of a solid. Dynamic SIMS probes the constituents present at the surface and below through the removal of many layers per analytical cycle. This is carried out using primary ion beams of significantly higher current densities. This form of SIMS also introduces the possibility to derive depth distributions of any element and in some cases, molecular species with relative ease. The ability to derive molecular depth profiles and even three-dimensional images is a recent advent introduced using large cluster primary ion sources on specific substrates. 

Cluster Ion SIMS Dynamic SIMS in its traditional form typically does not provide molecular information. Recent studies have, however, revealed that using large cluster primary ions, molecular depth profiles and even images in all three dimensions can be collected. 

The application of SIMS can broadly be subdivided into two modes, that being Static SIMS and Dynamic SIMS. Static SIMS is a methodology used to examine the elemental and molecular distributions present over the outermost monolayer present on any solid. Dynamic SIMS examines the elemental and molecular distributions as a function of depth. Note The ability to examine molecular distributions is a relatively recent capability introduced through the implementation of large cluster primary ion beams. This has also opened up the possibility of three-dimensional imaging of molecular distributions. 

The one exception to the above rule is noted for large cluster primary ion impact. This is realized as the increased sputter yields noted under snch conditions allow the sputter front to approach or even snrpass the damage front. This only occurs under highly specific conditions with an example illnstrated in Figure 5.4(b). 

Cluster Ion SEMS A form of Dynamic SIMS in which large cluster primary ions are used... 

Indeed, the full potential of SIMS is yet to be reahzed. As an example, the recent introduction of large cluster primary ion sources has allowed for the mapping of organic molecules in all Three Dimensions (3D) to levels not possible with any other technique. Likewise, the incorporation of Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass filters has allowed for unprecedented mass resolution values (>100,000) to be reached. These are but a few of the new areas being researched. 

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